Overdrive for metal

[ViolenceOnTheRadio]

This is speculative but I'm using a rather basic overdrive.
An op amp multiplier with your typical input and output filters and some clipping diodes on the feedback path.
So far it sounds pretty good, I posted a clip in another thread and can get some good in your face sounds and it's a medium gain when maxed.
But will I be able to overdrive such a circuit hard enough with a gain stage in front of it to push it into hard clipping for metal or am I just going to get unusable distortion?

[Fender3D]

more or less "metal" pedals use several cascade od stages.
you must somewhat tame down first stages in order to achieve a proper decent s/n ratio and distortion

[ViolenceOnTheRadio]

So far I'm only having frequency issues. I've been upping the gain and end up with treble or bass that has that shattered sound or unwanted frequencies I've filtered out in a previous stage are suddenly resurrected. I think the best solution since I am just winging it in advancing the design will be to implement variable high and low pass filters on trim pots for each stage so I'm not backtracking work and dealing with the nightmare of unsoldering parts on breadboard and alligator clipping in new ones until I find a curing value.

I have a protoboard but...I also have the hands of Sasquatch making it an incredibly unpleasant experience which is why I tend to have a lot of somewhat mundane questions. This is the circuit with the filters emitted. It's literally straight out of the book. My intention is to cascade 3 of these soft clipping stages, use a pot to control the gain of the first(which won't have the clipping diodes) and trim pots to set fixed gain on the second two then feed the trio through a tone stack.

[amptramp]

You might not need an elaborate filter.  Some units like the Tube Screamer use a capacitor across the diodes to roll off the high frequencies and also limit the amount of distortion applied to the high frequencies.  A capacitor from output to non-inverting input also promotes stability.  You might also consider resistors in series with the diodes to lessen the clipping effect in the second of the three stages and possibly the third.

If the circuit is symmetrical, there will be only odd harmonics added.  If the clipping is not symmetrical (different diodes or series resistors), even harmonics will be added, giving some of the effect of an octave up.  For example, if you play A 220 into a symmetrical clipper, you will get E 660 and C# 1100 as your main spectral additions, which is a nice major chord.  With asymmetrical clipping, you get A440 and A880 as well which may give you those towering metal chords that will make your eardrums meet in the centre of your head.  And don't forget to wear earplugs whn you are playing metal - not to keep the sound out, but to keep the blood from dripping out of your ears.  Yeah, baby, that's metal!

[Quackzed]

you could alternatively, just unhook the diodes from their left sides and reconnect them to ground for a diode to ground 'hard clipping' type distortion... or hook up a spdt switch ,middle lug to the diodes left ends, one side to where they are connected now, and the other side to ground, so you could switch them between being in the feedback path, and being tied to ground.  soft/hard clipping switch.

[edvard]

You might want to look at Mark Hammer's Chaos circuit.
http://hammer.ampage.org/files/Chaos.gif
That will give you some idea on how cascaded soft clipping can be used to do a Metal type sound.
Tweak to your liking...

[stringsthings]

This is speculative but I'm using a rather basic overdrive.
An op amp multiplier with your typical input and output filters and some clipping diodes on the feedback path.
So far it sounds pretty good, I posted a clip in another thread and can get some good in your face sounds and it's a medium gain when maxed.
But will I be able to overdrive such a circuit hard enough with a gain stage in front of it to push it into hard clipping for metal or am I just going to get unusable distortion?

what type of metal sound are you attempting to achieve?

[petemoore]

  I say build yourself a Gus's NPN boost or the other one...
  Then the Fetzer [or the fetzer]
  Since you have an OA FB Clipping stage, a bit of slightly dirtied boosted signal will probably light it fully without 'chokin'.
  Then thinking about voicing [use clip-wire-clip between ground/capacitor/and...put your LP filter here and there ..signal path points only...anywhere along what you have or have added, start sprinkling or taking notes on what dulls, what smooths [sorry for the adjectives] to decided about where and maybe get an idea how much to LP.
  Same basic thing for staging caps and HP voicing.
  Then..metal..mid scoop..probably = notch filter.
  But I'd go to Duncans TSC and figure the voicing is worth as much trouble as the clipping/boosts/amounts etc.
  Almost done or done, how's the output level...stick another Jfet here as recovery [or other active]?
  Fiddlie with the diode thresholds and boost settings [boost settings are easier to change if you have no diode switching switch, try assymetric>Symmetric...and the other other ones...take notes in an attempt to choose some dern values instead of diddlin' all day with it, put the switch in probably, figure the boost/input level to diodes makes difference like threshold change so...work with the symmetry/assymetry enough where you can hear it or more then use the pre-boost for nearsame effect as threshold change.
  Then do it again, and again, and again, exactly or not the same at all [not the same, but keep your intuition and some of the circuit fragments [stages you have built] so you get some use from the stuff>
  Fetzer Valve, Jfet Buffer, Duncans TSC, DIst+...what the heck..FF, Jfet stratoblaster to name a very very few worth looking at, divide the BMP into 4 stages +TC for another good looking at.   

[ViolenceOnTheRadio]

All very interesting Pete but the purpose of the project is to produce a completely unique design I can eventually transfer to PCB, assemble and sell as an amplifier or stand alone preamp. So far it sounds incredible overdriving amps and completely noise free, I just need more gain and rather than waste the parts and time, figured I would get some opinions on whether stacking gains of this design would produce hard clipping suitable for metal. I've just omitted the filtering I'm using since it's all unique in design. I have a filter on the input, the feedback path, the output and then a very unique 2 band EQ filter on the second stage which I designed. The master EQ however is simply a variation on the Fender tone stack.
Here's a sound clip of the circuit so far which I consider to be a medium gain. This is the sound run through the Fender tone stack then my cabinet voicing circuit patched directly into the mixing board.

http://www.supload.com/listen?s=ZzK67W

So far so good, just needs more gain to be used as a metal/hard rock solo distortion.
The version recorded is that basic circuit. The first stage is without the clipping diodes fed into the version posted as the second stage with the clipping diodes and of course, the filtering I've omitted from the schematic. Currently when I use it to overdrive an amp, I get a killer "aww" sound if I zero the treble and dime the bass.

[anchovie]

completely unique design

Good luck with that!

sell

Will there be royalties for the people on this DIY/hobbyists forum helping you with this R&D?

[lazerphea]

[ViolenceOnTheRadio]

completely unique design

Good luck with that!

sell

Will there be royalties for the people on this DIY/hobbyists forum helping you with this R&D?

Royalties for general observations....hmmm that sure would be nice!
I've really no intention of modifying the design. Just wanted to know if the foundation was a good building block for a more complex gain cascade. It's a really bizarre build from the unorthodox components I'm using such as the type of diodes for clipping to the bizarre 2 band EQ I came up with by modifying a variable high pass filter with extra resistors, caps and pots. In all my years of looking over hundreds if not thousands of schematics I've not come across anything like it. It's the ultimate cheese circuit!

I must admit though, the hard clipping everyone has mentioned will probably be necessary based on the recent tests I've done. Getting hard clipping from a soft clip cascaded design means adding way too many components.